1. Field of the Invention
This invention pertains to positioning determining devices, and in particular to devices that enable the position of a person to be determined relative to another person wherein a global positioning system receiver is used to determine the distance, direction and possible elevation distance between another global position receiver with the two devices interacting directly with each other not requiring a monitoring station.
2. Description of the Related Art
There have been many attempts in the past to construct and market an electronic tether. The most common forms of these products have used radio frequency (RF) transmitters and receivers. In this prior art, an individual (subordinate) would carry a portable RF transmitter that would periodically emit an RF signal that would be received by a master unit. The master unit relied upon the signal strength of the RF transmission to determine the proximity of the subordinate unit. If the received signal strength was less than a predefined level, an alert was sounded. These devices lacked the sophistication necessary to accurately determine distance between the subordinate unit and master unit or where the subordinate unit was in relation to the master unit. It is to be understood that a typical master unit would be a parent and a subordinate unit would be a child. A typical environment would be in the wilderness, theme park, shopping mall or in a crowded city.
Recent technology developments permit the monitoring of an individual""s location by incorporating a Global Positioning System (GPS). Global positioning uses satellites that are able to accurately fix an individual""s location within a few feet in distance. However, the use of this technology has, in the past, required the user to subscribe to monthly monitoring services. Such a method does not and cannot address the need for a parent, guardian or caregiver to be notified immediately if the individual under their supervision has traveled beyond a safe predetermined distance. Further, this method does not facilitate the use of location identification as a portable, use as needed, monitoring device. Another use of the GPS is to use two portable devices, master and subordinate, each equipped with a GPS receiver and the capability of the subordinate unit to transmit its location as defined by signals it receives from the GPS. In this implementation, the ability to locate an individual is dependent upon the fact that both the caregiver and the supervised individual""s device must be receiving GPS signals.
The prior art systems have many disadvantages. First, with reference to a device that relies solely on signal strength to determine range, these devices cannot compensate for signal strength variations that occur in one""s surroundings. That is to say, RF signals do not always arrive at a receiver with predictable strength in all locations. We know, for example, that signal strength at a particular distance in open space will be significantly different from the same transmitter when it is moved from open space to compartmentalized spaces of buildings. Therefore, an individual, such as a child, moving from an open play area within his safe zone to a playground maze or other type of structure, also within his safe zone, may cause nuisance type alarms because of signal attenuation. Secondly, devices that rely solely on data received from GPS satellites are subject to the availability of the GPS signal. However, depending upon the terrain and other obstructions, a temporary loss of signal can and does occur. In this situation, there would be an inactive period until the GPS receiver reacquires position information. During this temporary interruption of signal, the whereabouts of the child would be unavailable.
The system of this invention uses GPS receivers combined with RF transceivers and proprietary software. Both master and subordinate portable units are composed of a GPS receiver, RF transceiver, power supply, electronic compass, user interface and microprocessor. The units of this invention may be packaged as user wearable compact devices. In another embodiment, the master unit of this invention is capable of being connected to a fixed position base unit that is interfaced with a personal computer.
The operation of the system of this invention begins with the programming of the master unit and its associated subordinate unit(s). By utilizing the user interface, the units are placed in a program mode. This program mode facilitates the identifying of subordinate unit(s) by the master unit, and the identification of the master unit by the subordinate unit(s). Unique identification information contained in each master and subordinate unit are exchanged during the set-up stage of the user program. The information exchanged is kept in memory of the master and subordinate units. The exchange and storage of this information is to assure that when multiple users of the invention are in close proximity to each other that only those units programmed to be a xe2x80x9cfamilyxe2x80x9d will communicate with each other. While in the programming mode, the master unit will identify each subordinate""s unique identification number and will place in memory the identification number for each subordinate unit in its family. Subsequent to programming the master and subordinate unit(s) as a family, the master unit is programmed through the user interface to alert the master if the subordinate unit(s) has traveled beyond a selected distance. The user selected distances, of pre-established values have been optimized for system accuracy. In some embodiments of the subordinate unit(s), it is possible to program similar distance monitoring, measurement and notification as that of the master unit.
Once placed in service, the master and subordinate unit(s) will acquire information from the available GPS satellites. This data is placed in temporary memory. Upon completion of the acquisition process, the master unit will begin polling or interrogating the subordinate unit(s) by means of the RF transceiver. The subordinate unit(s) receiving the request from the master unit will respond by means of the RF transceiver, with the current or stored GPS coordinates. Included in this transmission will be the time that those coordinates were stored in temporary memory and the time of the response (transmission) to the polling request. Upon receipt of the polling response from the subordinate unit(s) by means of its RF transceiver, the master unit will calculate the distance to the subordinate unit(s) based upon the coordinates of the subordinate(s) with regard to the current coordinates of the master unit, compare that distance to the selected allowable range, and immediately display, and continuously display, the distance to and direction of travel to each subordinate unit. This process continues as long as the devices are in service. The continuing process of polling, receiving and calculating distance provides constant visual indication of the distance to a subordinate unit with regard to the position of the master unit. Depending upon the type of display used in a master unit, the location information of each subordinate unit may scroll automatically or manually at the discretion of the master user. As an important part of this invention, the proprietary software not only references the calculated distance to each subordinate unit against the user selected allowable range, but will reference the time associated with the coordinates that were transmitted by the subordinate unit(s) response.
The time associated with the received coordinates of a subordinate unit may be critical in determining the validity of the calculated distance to the subordinate unit(s). Whereas GPS signal availability could become temporarily unavailable, system design provides for alternate methods of determining distance that can be used in redundancy with valid GPS data or can determine distance independently of the availability of the GPS data. As previously stated, the devices will acquire data from available GPS satellites. This data is stored in temporary memory of the master and subordinate unit(s). At periodic intervals determined by the proprietary software, each unit receives new GPS data and replaces previously stored GPS coordinates with fresh data. Each time data from the GPS is placed in temporary memory, the time of that data is also placed in temporary memory. As the master unit queries a subordinate unit, the subordinate unit will respond with a fresh set of coordinates as it is being received from the GPS satellites. Should the subordinate unit be in a location where GPS signal is temporarily unavailable for the current coordinates at the time it is being queried, it will transmit the coordinates that have been stored in temporary memory along with the time that the coordinates were received and stored. The master unit, upon receipt of the subordinate unit response, will compare the received information time stamp to current time and determine if it is current data or stored data according to the time variance. The proprietary software will determine if the data is acceptable as current, according to predefined safety windows. If the data is accepted as valid current data, the master unit calculates the distance to the subordinate unit with regard to the current location coordinates of the master unit. The distance and direction to the subordinate unit(s) is displayed on the master unit.
In the event that the proprietary software of the master unit determines that the received coordinates from the subordinate unit is too old, it will again query the same subordinate unit(s) in an effort to gain current GPS coordinates. If the subordinate fails to respond with an acceptable time stamp return of coordinates for calculation by the master unit, the master unit will evaluate the received signal from the subordinate unit(s) according to time of arrival of the response with reference to the time of the request and determine distance according to algorithms established for this purpose. The master unit will then compare the results of this algorithmic procedure to the distance calculated by the last received GPS coordinates, and if determined to be similar in distance, and within the defined safe zone, continue to display the distance to and direction to travel to the subordinate unit. In the event that the master unit determines that the calculated distances of the two methods exceed the parameters of acceptability, an alert signal will be initiated on the master unit. The user display will indicate the last known distance to and direction to travel to reach the subordinate unit(s). The alert indication will remain active until the master unit receives current data that is calculated by either or both methods of range determination to be acceptable. Polling of units that are in the acceptable range with valid coordinates continue to be updated as normal during the alert caused by one or more of the subordinate units.
In addition to the master units ability to continuously display the distance and direction to travel to subordinate unit(s), the subordinate unit(s) will display the distance and direction to travel to the master unit. In one embodiment, the subordinate unit is enabled to display the information in the following method: In the normal polling cycle initiated by the master unit, the subordinate is requested to respond with it""s coordinates. The master unit receives the data, performs the calculation routine, determines distance and direction to travel to that subordinate unit and displays that information on it""s own display. Now, facilitated by the unique address of each subordinate unit that is retained in memory, the master unit will transmit a data stream to the subordinate unit that consists of the distance between the subordinate unit and the master unit, and the direction to travel to reach the master unit. This information is then displayed on the subordinate unit.
In another embodiment of this invention, the master unit transmits its"" coordinates during each polling cycle, and each so enabled subordinate unit, containing similar processing capabilities as that of the master unit, will calculate and display the distance and direction to travel to reach the master unit.
Both master and subordinate units contain an emergency call feature whereby the user may manually trigger an RF transmission causing the current or last stored location to be transmitted from the master to the subordinate, or from subordinate to master causing an alert at the other unit. When initiated by the master unit, the user may selectively call a particular subordinate unit, or all of the subordinate units within the family. When activated, the master unit will send information to the subordinate unit(s) that includes distance and direction to travel to reach the master user. When the subordinate unit initiates a call alert, the alert indication is activated at the master unit and information is refreshed at the master unit as to the current location of the subordinate unit. Also included in the displayed information on the master unit is the identification of the subordinate unit that activated the alert. As in other operating conditions,the devices continue to update location information as the master unit moves toward the location of the subordinate unit and the subordinate unit moves in the direction of the master unit.
Subordinate units in some embodiments of this invention employ the use of a tamper or supervisory switch that provides notification to the master unit should the wearer of the subordinate unit remove the unit from their body after the system has been put in use. As in other transmissions, the notification is in the form of an RF transmission containing the distance to and direction of travel to the subordinate unit based upon the last stored or current location data. The display on the master unit will indicate from which subordinate unit (s) the tamper alert was initiated. As in other operating conditions, the devices continue to update location information as the master unit moves toward the location of the subordinate unit, and the subordinate unit moves in the direction of the master unit.
The master unit display is arranged so that the user, at a glance, can determine that all subordinate units within the family are actively reporting and are within the preset parameters of safety. The display will facilitate the monitoring of a plurality of subordinate units and display in sequence the distance and direction to travel to each subordinate unit. Subordinate units may be identified upon the display as alphanumeric or by the use of icons. The master unit display will be capable of indicating several supervisory conditions that are transmitted from the subordinate units during routine polling cycles. These supervisory conditions include, but are not limited to loss of signal, low battery and tamper.
The proprietary communications protocol of the invention dictates the rate or frequency of the polling cycle of the subordinate unit(s) by the master unit. This polling rate has been optimized to maximize the battery life of the units. Provisions are made for the polling rate to be accelerated during events that demand more frequent location updates. These events include, but are not limited to: preprogrammed distance exceeded, activation of the emergency call feature, activation of the supervisory switch and loss of signal from any unit. When the polling rate has been accelerated due to any or all of these conditions, the alert indication at the master and subordinate unit(s) is temporarily inhibited to avoid nuisance alarm. Upon the verification of the unacceptable condition through subsequent exchanges of data, or lack of data, during the accelerated polling cycle, the appropriate alert signal is initiated. The master unit will continue polling at the accelerated rate, updating information from the subordinate unit(s) that caused the alert condition. This process continues until such time that the alert condition has been resolved and manually acknowledged by the user of the master unit. Following the resolution and acknowledgement, the units will return to the normal battery conserving polling rate.
During alert conditions, the master unit will continuously update the information on its display so as to facilitate prompt location of the subordinate unit. The master unit transmission to the subordinate unit will also update the distance and direction the subordinate unit is to travel to reach the master unit.
The units operate on approved RF channels, and the transmission schemes utilize a proprietary digital communications protocol to facilitate very short message packets. The polling cycle of the units is determined by the number of subordinate units under the supervision of the master.
Both the master and subordinate units are designed to make optimal use of their available battery power to minimize battery replacement or recharging. Preferred embodiments of both the master and the subordinate units may incorporate rechargeable battery sources, which do not require removal from the unit. The master unit being larger in size may employ the use of a plug-in charging device. The subordinate unit may employ a unique charging connection developed for this invention. The strap or connection used to attach the subordinate unit to the child or person being supervised may perform the dual service of a tamper device and as the connection to the battery charger. In normal operation, the strap or connector is a closed loop tamper switch. When recharging of the battery is necessary, the open ends of the strap or connector will be inserted into a special charging device.
Additionally, to further conserve battery life when the subordinate unit is not being used, it is desirable to turn off all or a portion of the functions of the subordinate unit. However, due to the nature of this device, it is impractical to provide for a simple on/off switch which could be activated by the child. In a preferred embodiment of the system, the subordinate unit could be powered on by depressing a switch on the subordinate unit. To power down the subordinate unit would require a power down command to be entered through the user interface of the master unit. The master unit would then transmit a properly coded power down instruction to the subordinate unit which would receive the transmission and verify its authenticity before powering down.
It is the object of this invention to overcome the weaknesses of the prior art inventions so that a parent, guardian or caregiver may monitor the location of the child or individual under their supervision with confidence.
It is the object of this invention to overcome the weakness of radio transmitting devices that measure signal strength. It is a known fact that such devices that rely solely upon signal strength for distance measurement are less than reliable at times. Due to various conditions, such as building construction, other radios in close proximity, secondary reflections caused by stationary or moving objects or even trees in heavily wooded areas, received signals can vary significantly in strength.
The subject invention eliminates the need for central station monitoring and the fees associated with such a service.
It is also the object of this invention to reduce the time involved to locate a child or other person using the device by presenting the information necessary to resolve the alarm to both the caregiver and the subordinate user simultaneously.
It is also an objective of this invention to overcome a loss of GPS signal. In such an instance, the master unit and subordinate unit are capable of referring back to the previously stored GPS signal which has been retained in memory. The referring to prior GPS location signals from the memory is to occur only for a certain pre-established period of time. Once that time is exceeded and still a current GPS signal can not be received, both the master unit and the subordinate unit will utilize an alternate method of distance determination, such as time interval measurement.